1. Field of the invention
This invention relates to a deionized water supplying system, and more particularly to a deionized water supplying system suitable for preventing impurities from entering into the deionized water.
2. Description of the related art
In the manufacture of miniaturized LSI devices, a deionized water supplying system plays an important role in the wafer process.
In the deionized water supplying system, unused deionized water having passed through a use point of the water process is refined and supplied to the use point again. This method is called the circulating method.
FIGS. 1(a) and 1(b) show a conventional deionized water supplying mechanism used in the deionized water supplying system, such as that described in Japanese Patent Publication No. 151026/1983.
In these figures, a two-ported valve 3 is connected to a deionized water tank 4 for the wafer cleaning process and two branch pipes 2 and 7 associated with a three-forked pipe 6. A maintenance valve 8 illustrated in FIG. 1(b) is used for replacing the valve 3. Further, the conductance of branch pipe 7 is less than that of branch pipe 2.
When the deionized water tank 4 need not be supplied with deionized water, unused deionized water flows from a deionized water supplying pipe 1 to a deionized water circulating pipe 5 via branch pipes 2 and 7 and three-forked pipe 6.
During the wafer cleaning process, the two-ported valve 3 is opened and according to the difference of the conductance, the greater part of deionized water flows from the deionized water supplying pipe 1 to the deionized water tank 4 via the two-ported valve 3.
However, the conventional mechanism described above has disadvantages that while the two-ported valve 3 is closed, a quantity of deionized water normally remains between the two-ported valve 3 and the three-forked pipe 6.
Although the distance between two-ported valve 3 and three-forked pipe 6 is about 20-90 cm, if the holdup of deionized water lasts a long time, bacteria or microbes will breed and cause the contamination of the deionized water supplying system.